apparently within the bounds of possibility. Could we stop here we should
be fairly contented. But, to complete the system, to carry out the
principles to their ultimate conclusion, and to explain by them many facts
in geographical distribution which would still remain anomalous, Mr. Darwin
is equally bound to account for the formation of genera, families, orders,
and even classes, by natural selection. He does "not doubt that the theory
of descent with modification embraces all the members of the same class,"
and he concedes that analogy would press the conclusion still further;
while he admits that "the more distinct the forms are, the more the
arguments fall away in force." To command assent we naturally require
decreasing probability to be overbalanced by an increased weight of
evidence. An opponent might plausibly, and perhaps quite fairly, urge that
the links in the chain of argument are weakest just where the greatest
stress falls upon them.

To which Mr. Darwin's answer is, that the best parts of the testimony have
been lost. He is confident that intermediate forms must have existed; that
in the olden times when the genera, the families, and the orders, diverged
from their parent stocks, gradations existed as fine as those which now
connect closely related species with varieties. But they have passed and
left no sign. The geological record, even if all displayed to view, is a
book from which not only many pages, but even whole alternate chapters,
have been lost out, or rather which were never printed from the autographs
of Nature. The record was actually made in fossil lithography only at
certain times and under certain conditions (i.e., at periods of slow
subsidence and places of abundant sediment); and of these records all but
the last volume is out of print; and of its pages only local glimpses have
been obtained. Geologists, except Lyell, will object to this--some of them
moderately, others with vehemence. Mr. Darwin himself admits, with a candor
rarely displayed on such occasions, that he should have expected more